Method for transmitting and receiving channel state information in wireless communication system and apparatus therefor

ABSTRACT

A method for a machine type communication (MTC) terminal to report a channel state information (CSI) in a wireless communication system, according to an embodiment of the present invention, comprises the steps of: selecting a set of M downlink subframes as a CSI reference resource for the MTC terminal; measuring a channel quality indicator (CQI) through the CSI reference resource; and transmitting a CSI report including the CQI to a base station through an uplink subframe, wherein the MTC terminal is configured to repeatedly receive an MTC signal by frequency-hopping N sub-bands among a plurality of sub-bands. The number ‘M’ of the downlink subframes to be included in the CSI reference resource is determined on the basis of an upper layer parameter received from the base station. Further, the MTC terminal may measure the CQI on the basis of a cell-specific reference signal (CRS) received through the M downlink subframes selected from a reference downlink subframe located before the uplink subframe.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Phase of PCT International ApplicationNo. PCT/KR2016/009191, filed on Aug. 19, 2016, which claims priorityunder 35 U.S.C. 119(e) to U.S. Provisional Application No. 62/207,943,filed on Aug. 21, 2015, all of which are hereby expressly incorporatedby reference into the present application.

TECHNICAL FIELD

The present invention relates to a method of transmitting or receiving achannel state information report in a wireless communication systemsupporting machine type communication (MTC), and an MTC user equipment(UE) and a base station for performing the same.

BACKGROUND ART

Wireless communication systems have been widely deployed to providevarious types of communication services such as voice or data. Ingeneral, a wireless communication system is a multiple access systemthat supports communication of multiple users by sharing availablesystem resources (a bandwidth, transmission power, etc.) among them. Forexample, multiple access systems include a Code Division Multiple Access(CDMA) system, a Frequency Division Multiple Access (FDMA) system, aTime Division Multiple Access (TDMA) system, an Orthogonal FrequencyDivision Multiple Access (OFDMA) system, a Single Carrier FrequencyDivision Multiple Access (SC-FDMA) system, and a Multi Carrier FrequencyDivision Multiple Access (MC-FDMA) system. In a wireless communicationsystem, a User Equipment (UE) may receive information from a BaseStation (BS) on a Downlink (DL) and transmit information to the BS on anUplink (UL). The UE transmits or receives data and various types ofcontrol information. Various physical channels exist according to thetypes and usages of information that the UE transmits or receives.

DISCLOSURE Technical Problem

An object of the present invention is to provide a method of moreefficiently or accurately measuring and transmitting or receivingchannel state information in a wireless communication system supportingMTC and an apparatus for performing the same.

Technical tasks obtainable from the present invention are non-limitedthe above mentioned technical tasks and other unmentioned technicaltasks can be clearly understood from the following description by thosehaving ordinary skill in the technical field to which the presentinvention pertains.

Technical Solution

The object of the present invention can be achieved by providing amethod of reporting channel state information (CSI) at a machine typecommunication (MTC) user equipment (UE) in a wireless communicationsystem including selecting a set of M downlink subframes as a CSIreference resource for the MTC UE, measuring a channel quality indicator(CQI) through the CSI reference resource and transmitting a CSI reportincluding the CQI to a base station through an uplink subframe, whereinthe MTC UE is configured to repeatedly receive an MTC signal byfrequency hopping N subbands among a plurality of subbands, wherein ‘M’which is a number of downlink subframes to be included in the CSIreference resource is determined based on a higher layer parameterreceived from the base station, and wherein the MTC UE measures the CQIbased on a cell-specific reference signal (CRS) received through the Mdownlink subframes selected from a reference downlink subframe locatedbefore the uplink subframe.

In another aspect of the present invention, provided herein is a machinetype communication (MTC) user equipment (UE) for reporting channel stateinformation (CSI) in a wireless communication system including aprocessor for selecting a set of M downlink subframes as a CSI referenceresource for the MTC UE and measuring a channel quality indicator (CQI)through the CSI reference resource and a transmitter for transmitting aCSI report including the CQI to a base station through an uplinksubframe, wherein the MTC UE is configured to repeatedly receive an MTCsignal by frequency hopping N subbands among a plurality of subbands,wherein ‘M’ which is a number of downlink subframes to be included inthe CSI reference resource is determined based on a higher layerparameter received from the base station, and wherein the processormeasures the CQI based on a cell-specific reference signal (CRS)received through the M downlink subframes selected from a referencedownlink subframe located before the uplink subframe.

In another aspect of the present invention, provided herein is a methodof receiving a channel state information (CSI) report at a base stationfrom a machine type communication (MTC) user equipment (UE) in awireless communication system including transmitting a cell-specificreference signal (CRS) through downlink subframes, and receiving a CSIreport including a channel quality indicator (CQI) measured in a CSIreference resource from the MTC UE through an uplink subframe, whereinthe base station repeatedly transmits an MTC signal by frequency hoppingN subbands among a plurality of subbands, wherein the CSI referenceresource is configured as M downlink subframes among the downlinksubframes in which the CRS is transmitted, wherein which is a number ofdownlink subframes included in the CSI reference resource is determinedbased on a higher layer parameter transmitted by the base station, andwherein the CQI is measured based on a cell-specific reference signal(CRS) transmitted through the M downlink subframes selected from areference downlink subframe located before the uplink subframe.

In another aspect of the present invention, provided herein is a basestation apparatus for performing the method of receiving the CSI report.

The M downlink subframes included in the CSI reference resource may bevalid downlink subframes.

The reference downlink subframe may be located before the uplinksubframe by at least four subframes.

The CQI may be measured with respect to all of the N subbands.

The CQI may be measured with respect to any one of the N subbands.

The measuring of the CQI may include measuring the CQI by assuming thatthe same redundancy version is applied to the M downlink subframes whenone physical downlink shared channel (PDSCH) transport block isrepeatedly received through the M downlink subframes.

The measuring of the CQI may include measuring the CQI by assuming thatthe same redundancy version is 0 and rank between the base station andthe MTC UE is always 1.

The measuring of the CQI may include selecting a highest CQI index valuefrom among predetermined CQI indices in which an error probability ofthe PDSCH transport block does not exceed 0.1, when the PDSCH transportblock is repeatedly received through the M downlink subframes.

Advantageous Effects

According to embodiments of the present invention, since a CSI referenceresource is configured to include M subframes in consideration ofrepeated transmission properties of an MTC signal in a wirelesscommunication system supporting MTC, channel state information may bemore efficiently and accurately measured and reported.

It will be appreciated by persons skilled in the art that the effectsthat can be achieved through the present invention are not limited towhat has been particularly described hereinabove and other advantages ofthe present invention will be more clearly understood from the followingdetailed description.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiments of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 illustrates physical channels and a general signal transmissionmethod using the physical channels in a Long Term Evolution(-Advanced)(LTE-(A)) system.

FIG. 2 illustrates a radio frame structure in the LTE(-A) system.

FIG. 3 illustrates a resource grid for the duration of a slot.

FIG. 4 illustrates an exemplary Downlink (DL) SubFrame (SF) structure.

FIG. 5 illustrates an example of allocating Enhanced Physical DownlinkControl Channels (E-PDCCHs) to an SF.

FIG. 6 illustrates an Uplink (UL) SF structure.

FIG. 7 is a conceptual diagram illustrating exemplary DiscontinuousReception (DRX).

FIG. 8 is a conceptual diagram illustrating a Random Access Procedure(RAP).

FIG. 9 is a conceptual diagram illustrating Cell-specific ReferenceSignal (CRS).

FIG. 10 is a diagram illustrating a UE selected CQI report mode.

FIG. 11 is a diagram illustrating a wideband CQI of an MTC UE accordingto an embodiment of the present invention.

FIG. 12 is a diagram showing a set of subframes for CSI referenceresources according to an embodiment of the present invention.

FIG. 13 is a diagram illustrating a reference downlink subframeaccording to an embodiment of the present invention.

FIG. 14 is a flowchart illustrating a CSI reporting method according toan embodiment of the present invention.

FIG. 15 is a diagram showing a base station and a UE applicable to anembodiment of the present invention.

BEST MODE

Reference will now be made in detail to the exemplary embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The detailed description, which will be given below withreference to the accompanying drawings, is intended to explain exemplaryembodiments of the present invention, rather than to show the onlyembodiments that can be implemented according to the present invention.The configuration, operation, and other features of the presentinvention will readily be understood with embodiments of the presentinvention described with reference to the attached drawings. Embodimentsof the present invention may be used for various radio access systemssuch as Code Division Multiple Access (CDMA), Frequency DivisionMultiple Access (FDMA), Time Division Multiple Access (TDMA), OrthogonalFrequency Division Multiple Access (OFDMA), Single Carrier FrequencyDivision Multiple Access (SC-FDMA), Multi-Carrier Frequency DivisionMultiple Access (MC-FDMA), etc. CDMA may be implemented as a radiotechnology such as Universal Terrestrial Radio Access (UTRA) orCDMA2000. TDMA may be implemented as a radio technology such as GlobalSystem for Mobile communications/General packet Radio Service/EnhancedData Rates for GSM Evolution (GSM/GPRS/EDGE). OFDMA may be implementedas a radio technology such as Institute of Electrical and ElectronicEngineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20,Evolved UTRA (E-UTRA), etc. UTRA is a part of Universal MobileTelecommunications System (UMTS). 3^(rd) Generation Partnership ProjectLong Term Evolution (3GPP LTE) is a part of Evolved UMTS (E-UMTS) usingE-UTRA, and LTE-Advanced (LTE-A) is an evolution of 3GPP LTE.

While the embodiments of the present invention will be described belowmainly in the context of a 3GPP system, this is purely exemplary andthus should not be construed as limiting the present invention.

While the present invention is described in the context of an LTE-Asystem, the proposed concept or methods of the present invention andembodiments of the proposed concept or methods are applicable to othermulti-carrier systems (e.g., an IEEE 802.16m system) withoutrestriction.

FIG. 1 illustrates physical channels and a general method fortransmitting signals on the physical channels in an LTE(-A) system.

Referring to FIG. 1, when a User Equipment (UE) is powered on or entersa new cell, the UE performs initial cell search in step S101. Theinitial cell search involves acquisition of synchronization to anevolved Node B (eNB). Specifically, the UE synchronizes its timing tothe eNB and acquires a cell Identifier (ID) and other information byreceiving a Primary Synchronization Channel (P-SCH) and a SecondarySynchronization Channel (S-SCH) from the eNB. Then the UE may acquireinformation (i.e., a Master Information Block (MIB)) broadcast in thecell by receiving a Physical Broadcast Channel (PBCH) from the eNB.During the initial cell search, the UE may monitor a Downlink (DL)channel state by receiving a DownLink Reference Signal (DL RS).

After the initial cell search, the UE acquires detailed systeminformation (i.e. a System Information Block (SIB)) by receiving aPhysical Downlink Control Channel (PDCCH) and receiving a PhysicalDownlink Shared Channel (PDSCH) based on information included in thePDCCH in step S102.

Then, the UE may perform a random access procedure with the eNB tocomplete the connection to the eNB in step S103 to S106. In the randomaccess procedure, the UE may transmit a preamble on a Physical RandomAccess Channel (PRACH) (S103) and may receive a response message to thepreamble on a PDCCH and a PDSCH associated with the PDCCH (S104). In thecase of contention-based random access, the UE additionally performs acontention resolution procedure including transmission of a PhysicalUplink Shared Channel (PUSCH) (S105) and reception of a PDCCH and itsassociated PDSCH (S106).

After the above procedure, the UE may receive a PDCCH/PDSCH (S107) andtransmit a PUSCH/PUCCH (S108) in a general UL/DL signal transmissionprocedure.

FIG. 2 illustrates a radio frame structure in the LTE(-A) system. The3GPP LTE standards support a type 1 radio frame structure applicable toFrequency Division Duplex (FDD) and a type 2 radio frame structureapplicable to Time Division Duplex (TDD).

FIG. 2(a) is a diagram illustrating the structure of the type 1 radioframe. An FDD radio frame includes only DL subframes or only ULsubframes. The radio frame includes 10 subframes, each subframeincluding two slots in the time domain. One subframe may be 1 ms longand one slot may be 0.5 ms long. One slot includes a plurality of (DL)OFDM symbols or a plurality of (UL) SC-FDMA symbols in the time domain.Unless specifically mentioned, “OFDM symbol” or “SC-FDMA” symbol may bereferred to simply as “symbol” (hereinafter referred to as ‘sym’).

FIG. 2(b) illustrates the structure of the type 2 radio frame. A TDDradio frame includes two half frames, each half frame including four(five) general subframes and one (zero) special subframe. The generalsubframes are used for UL or DL according to a UL-DL configuration andthe special subframe includes a Downlink Pilot Time Slot (DwPTS), aGuard Period (GP), and an Uplink Pilot Time Slot (UpPTS). In the specialsubframe, DwPTS is used for initial cell search, synchronization, orchannel estimation at a UE. UpPTS is used for an eNB to perform channelestimation and acquire UL synchronization with a UE. The GP is used tocancel UL interference between a UL and a DL, caused by the multi-pathdelay of a DL signal. A subframe includes two slots.

[Table 1] lists exemplary subframe configurations for a radio frameaccording to UL-DL configurations.

TABLE 1 Downlink- to-Uplink Uplink- Switch- downlink point Subframenumber configuration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U DS U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms  DS U U U D D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D D DD D 6 5 ms D S U U U D S U U D

In [Table 1], D represents a DL subframe, U represents a UL subframe,and S represents a special subframe.

FIG. 3 illustrates a resource grid for the duration of one slot. A slotincludes a plurality of symbols (e.g., OFDM symbols or SC-FDMA symbols),for example, 6 or 7 symbols in the time domain by a plurality ofResource Blocks (RBs) in the frequency domain. Each RB includes 12subcarriers. Each element of a resource grid is called a ResourceElement (RE). The RE is a minimum resource unit for signal transmissionand one modulation symbol is mapped to an RE.

FIG. 4 illustrates a structure of a DL subframe. Up to 3 (or 4) OFDMsymbols at the start of the first slot of a DL subframe are used as acontrol region to which a control channel is allocated and the remainingOFDM symbols of the DL subframe are used as a data region to which ashared channel (e.g., a PDSCH) is allocated. DL control channels includea Physical Control Format Indicator Channel (PCFICH), a PDCCH, aPhysical Hybrid automatic repeat request (ARQ) Indicator Channel(PHICH), etc.

The PCFICH is located in the first OFDM symbol of a subframe, carryinginformation about the number of OFDM symbols used for transmission ofcontrol channels in the subframe. The PHICH occupies 4 RE Groups (REGs)distributed equally in the control region based on a cell Identifier(ID). The PCFICH indicates a value ranging 1 to 3 (or 2 to 4) and ismodulated in Quadrature Phase Shift Keying (QPSK). The PHICH delivers anHARQ ACKnowledgment/Negative ACKnowledgment (ACK/NACK) signal as aresponse to a UL transmission. The PHICH is allocated to the remainingREGs of one or more OFDM symbols corresponding to a PHICH duration,except for REGs carrying Cell-specific Reference Signals (CRSs) and thePCFICH (the first OFDM symbol). The PHICH is allocated to 3 REGsdistributed as much as possible in the frequency domain.

The PDCCH delivers information about resource allocation and a transportformat for a Downlink Shared Channel (DL-SCH), information aboutresource allocation and a transport format for an Uplink Shared Channel(UL-SCH), paging information of a Paging Channel (PCH), systeminformation on the DL-SCH, information about resource allocation for ahigher-layer control message such as a random access responsetransmitted on the PDSCH, a set of transmission power control commandsfor individual UEs of a UE group, a Transmit Power Control (TPC)command, Voice Over Internet Protocol (VoIP) activation indicationinformation, etc. A plurality of PDCCHs may be transmitted in thecontrol region. A UE may monitor a plurality of PDCCHs. A PDCCH istransmitted in an aggregate of one or more consecutive Control ChannelElements (CCEs). A CCE is a logical allocation unit used to provide aPDCCH at a coding rate based on the state of a radio channel. A CCEincludes a plurality of REGs. The format of a PDCCH and the number ofavailable bits for the PDCCH are determined according to the number ofCCEs.

[Table 2] lists the number of CCEs, the number of REGs, and the numberof PDCCH bits for each PDCCH format.

TABLE 2 Number of CCEs Number of PDCCH format (n) Number of REGs PDCCHbits 0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

The CCEs may be numbered consecutively and a PDCCH having a format withn CCEs may start only at a CCE with an index being a multiple of n. Thenumber of CCEs used for transmission of a specific PDCCH is determinedaccording to a channel condition by an eNB. For example, if the PDCCH isfor a UE having a good DL channel (e.g., a UE near to the eNB), one CCEmay be sufficient for the PDCCH. On the other hand, if the PDCCH is fora UE having a poor channel (e.g., a UE near to a cell edge), 8 CCEs maybe used for the PDCCH in order to achieve sufficient robustness. Inaddition, the power level of the PDCCH may be controlled according tothe channel condition.

Control information transmitted on a PDCCH is called Downlink ControlInformation (DCI). Various DCI formats are defined according to theusages of the DCI. Specifically, DCI formats 0 and 4 (a UL grant) aredefined for UL scheduling and DCI formats 1, 1A, 1B, 1C, 1D, 2, 2A, 2B,and 2C (a DL grant) are defined for DL scheduling. Depending on itsusage, a DCI format selectively includes information such as a hoppingflag, an RB assignment, a Modulation Coding Scheme (MCS), a RedundancyVersion (RV), a New Data Indicator (NDI), a TPC, a cyclic shift, aDeModulation Reference Signal (DM-RS), a Channel Quality Information(CQI) request, an HARQ process number, a Transmitted Precoding MatrixIndicator (TPMI), Precoding Matrix Indicator (PMI) confirmation, etc.

An eNB determines a PDCCH format according to control information to betransmitted to a UE and adds a Cyclic Redundancy Check (CRC) to thecontrol information, for error detection. The CRC is masked by an ID(e.g., a Radio Network Temporary Identifier (RNTI) according to theowner or usage of a PDCCH. In other words, the PDCCH is CRC-scrambledwith the ID (e.g., the RNTI).

[Table 3] lists exemplary IDs by which a PDCCH is masked.

TABLE 3 Type Identifier Description UE-specific C-RNTI, used for aunique UE identification TC-RNTI, SPS C-RNTI Common P-RNTI used forpaging message SI-RNTI used for system information RA-RNTI used forrandom access response

If a C-RNTI, a Temporary C-RNTI (TC-RNTI), and a Semi-PersistentScheduling C-RNTI (SPS C-RNTI) are used, the PDCCH delivers UE-specificcontrol information for a specific UE. If other RNTIs are used, thePDCCH delivers common control information for all UEs in a cell.

The LTE(-A) standard defines the CCE positions of a limited set(equivalent to a limited CCE set or a limited PDCCH candidate set) inwhich a PDCCH may be located, for each UE. The CCE positions of alimited set that a UE should monitor to detect a PDCCH directed to theUE may be referred to as a Search Space (SS). Monitoring includesdecoding each PDCCH candidate (blind decoding). A UE-specific SearchSpace (USS) and a Common Search Space (CSS) are defined. A USS isconfigured on a UE basis and a CSS is configured commonly for UEs. TheUSS and the CSS may be overlapped. The starting position of the USS hopsbetween subframes UE-specifically. An SS may have a different sizeaccording to a PDCCH format.

[Table 4] lists CSS sizes and USS sizes.

TABLE 4 Number of Number of PDCCH Number of CCEs PDCCH candidates PDCCHcandidates format (n) in CSS in USS 0 1 — 6 1 2 — 6 2 4 4 2 3 8 2 2

To place computation load under control according to the total number ofBlind Decodings (BDs), a UE is not required to detect all defined DCIformats at the same time. In general, the UE always detects formats 0and 1A in a USS. Formats 0 and 1A have the same size and aredistinguished from each other by a flag in a message. The UE may berequired to receive an additional format (e.g., format 1, 1B, or 2according to a PDSCH Transmission Mode (TM) configured by an eNB). TheUE detects formats 1A and 1C in a CSS. The UE may further be configuredto detect format 3 or 3A. Formats 3 and 3A have the same size as formats0 and 1A and may be identified by scrambling a CRC with different IDs(or a common ID), instead of UE-specific IDs.

PDSCH transmission schemes according to TMs and information content ofDCI formats are given as follows.

TMs

TM 1: transmission from a single eNB antenna port

TM 2: transmit diversity

TM 3: open-loop spatial multiplexing

TM 4: closed-loop spatial multiplexing

TM 5: Multi-User Multiple Input Multiple Output (MU-MIMO)

TM 6: closed-loop rank-1 precoding

TM 7: single-antenna port (port 5) transmission

TM 8: double-layer transmission (port 7 and port 8) or single-antennaport (port 7 or port 8) transmission

TMs 9 and 10: up to 8-layer transmission (port 7 to port 14) orsingle-antenna port (port 7 or port 8) transmission

DCI Formats

format 0: resource grant for PUSCH transmission

format 1: resource allocation for single-codeword PDSCH transmission(TMs 1, 2 and 7)

format 1A: compact signaling of resource allocation for single-codewordPDSCH (all modes)

format 1B: compact resource allocation for PDSCH (mode 6) using rank-1closed-loop precoding

format 1C: very compact resource allocation for PDSCH (e.g.,paging/broadcast system information)

format 1D: compact resource allocation for PDSCH using MU-MIMO (mode 5)

format 2: resource allocation for PDSCH of closed-loop MIMO operation(mode 4)

format 2A: resource allocation for PDSCH of open-loop MIMO operation(mode 3)

format 3/3A: power control command having 2-bit/1-bit power controlvalue for PUCCH and PUSCH

format 4: resource grant for PUSCH transmission in a cell set tomulti-antenna port transmission mode

DCI formats may be classified into a TM-dedicated format and a TM-commonformat. The TM-dedicated format is a DCI format configured for acorresponding TM only, and the TM-common format is a DCI formatconfigured commonly for all TMs. For example, DCI format 2B may be aTM-dedicated DCI format for TM 8, DCI format 2C may be a TM-dedicatedDCI format for TM 9, and DCI format 2D may be a TM-dedicated DCI formatfor TM 10. DCI format 1A may be a TM-common DCI format.

FIG. 5 illustrates an example of allocating Enhanced PDCCHs (E-PDCCHs)to a subframe. A legacy LTE system has limitations such as transmissionof a PDCCH in limited OFDM symbols. Accordingly, LTE-A has introducedthe E-PDCCH for more flexible scheduling.

Referring to FIG. 5, a PDCCH conforming legacy LTE(-A) (referred to as alegacy PDCCH or L-PDCCH) may be allocated to a control region (refer toFIG. 4). An L-PDCCH region means a region to which an L-PDCCH may beallocated. The L-PDCCH region may refer to a control region, a controlchannel resource region (i.e., CCE resources) to which a PDCCH may beactually allocated, or a PDCCH SS depending on the context. A PDCCH maybe additionally allocated to a data region (refer to FIG. 4). The PDCCHallocated to the data region is referred to as an E-PDCCH. Asillustrated in FIG. 5, a scheduling constraint imposed by the limitedcontrol channel resources of the L-PDCCH region may be relieved byadditionally securing control channel resources through the E-PDCCH. AnE-PDCCH and a PDSCH are multiplexed in Frequency Division Multiplexing(FDM) in the data region.

Specifically, the E-PDCCH may be detected/demodulated based on DM-RS.The E-PDCCH is transmitted in a Physical Resource Block (PRB) pair alongthe time axis. If E-PDCCH-based scheduling is configured, a subframe inwhich an E-PDCCH will be transmitted/detected may be indicated. TheE-PDCCH may be configured only in a USS. A UE may attempt to detect DCIonly in an L-PDCCH CSS and an E-PDCCH USS in a subframe allowed to carryan E-PDCCH (hereinafter, an E-PDCCH subframe) and in an L-PDCCH CSS andan L-PDCCH USS in a subframe not allowed to carry an E-PDCCH(hereinafter, a non-E-PDCCH subframe).

Like the L-PDCCH, the E-PDCCH delivers DCI. For example, the E-PDCCH maydeliver DL scheduling information and UL scheduling information. AnE-PDCCH/PDSCH operation and an E-PDCCII/PUSCII operation are performedin the same manner as/a similar manner to steps S107 and S108 of FIG. 1.That is, a UE may receive an E-PDCCH and receive data/controlinformation on a PDSCH corresponding to the E-PDCCH. In addition, the UEmay receive an E-PDCCH and transmit data/control information on a PUSCHcorresponding to the E-PDCCH. In the legacy LTE system, a PDCCHcandidate region (a PDCCH SS) is reserved in a control region and aPDCCH for a specific UE is transmitted in a part of the PDCCH SS.Therefore, a UE may detect its PDCCH in the PDCCH SS by blind decoding.Similarly, an E-PDCCH may also be transmitted in all or a part ofreserved resources.

FIG. 6 illustrates a structure of a UL subframe in the LTE system.

Referring to FIG. 6, a UL subframe includes a plurality of slots (e.g. 2slots). Each slot may include a different number of SC-FDMA symbolsaccording to a Cyclic Prefix (CP) length. The UL subframe is dividedinto a control region and a data region in the frequency domain. A PUSCHcarrying a data signal such as voice or the like is transmitted in thedata region, and a PUCCH carrying Uplink Control Information (UCI) istransmitted in the control region. The PUCCH includes an RB pair locatedat both ends of the data region along the frequency axis and hops over aslot boundary.

The PUCCH may carry the following control information.

Scheduling Request (SR): information used to request UL-SCH resources.The SR is transmitted in On-Off Keying (OOK).

HARQ response: a response signal to a DL data block (e.g., a TransportBlock (TB)) or a CodeWord (CW) on a PDSCH. The HARQ response indicateswhether the DL data block has been received successfully. A 1-bitACK/NACK is transmitted as a response to a single DL codeword and a2-bit ACK/NACK is transmitted as a response to two DL codewords. An HARQACK/NACK and an HARQ-ACK may be interchangeably used in the same meaningof an HARQ response.

Channel Quality Indicator (CSI): feedback information for a DL channel.MIMO-related feedback information includes an RI and a PMI. The CQIoccupies 20 bits per subframe.

The amount of UCI that a UE may transmit in a subframe depends on thenumber of SC-FDMA symbols available for transmission of the UCI. TheSC-FDMA symbols available for transmission of the UCI are the remainingSC-FDMA symbols except SC-FDMA symbols configured for transmitting RSsin the subframe. The last SC-FDMA symbol of a subframe configured tocarry an SRS is additionally excluded from the SC-FDMA symbols availablefor transmission of the UCI. An RS is used for coherent detection of aPUCCH. A PUCCH supports 7 formats according to information carried onthe PUCCH.

[Table 5] illustrates a mapping relationship between PUCCH formats andUCI in the LTE system.

TABLE 5 PUCCH format Uplink Control Information (UCI) format 1SR(Scheduling Request) (non-modulated waveform) format 1a bit HARQACK/NACK (SR present/absent) format 1b bit HARQ ACK/NACK (SRpresent/absent) format 2 CQI (20 coded bits) format 2 CQI and 1- or2-bit HARQ ACK/NACK (20 bits) (only in case of extended CP) format 2aCQI and 1-bit HARQ ACK/NACK (20 + 1 coded bits) format 2b CQI and 2-bitHARQ ACK/NACK (20 + 2 coded bits)

FIG. 7 is a conceptual diagram illustrating Discontinuous Reception(DRX). User equipment (UE) may perform DRX to reduce power consumption.DRX may control PDCCH monitoring activation of the UE. Referring to FIG.7, the DRX period may include one period denoted by “On duration” andthe other period denoted by “Opportunity for DRX”. In more detail, theUE may monitor PDCCH for the “On duration” period, and may not performPDCCH monitoring during the “Opportunity for DRX” period. The PDCCHmonitoring may include monitoring C-RNTI, TPC-PUCCH-RNTI, andTPC-PUSCH-RNT of the UE, and may further include monitoring SPS(Semi-Persistent Scheduling) C-RNTI of the UE (when configuration isachieved). If the UE is in the RRC (Radio Resource Control)_CONNECTEDstate and DRX is configured, the UE may perform discontinuous monitoringof PDCCH according to the DRX operation. Otherwise, the UE may performcontinuous monitoring of the PDCCH. “onDurationTimer” and DRX cycle maybe configured through RRC signaling (i.e., higher layer signaling).“onDurationTimer” may denote the number of successive PDCCH-subframesstarting from the start time of the DRX cycle. In FDD, the PDCCHsubframe may denote all subframes. In TDD, the PDCCH subframe may denotea subframe including both a downlink (DL) subframe and a DwPTS.

FIG. 8 illustrates a random access procedure. The random accessprocedure is used to transmit UL short data. For example, uponoccurrence of initial access in Radio Resource Control (RRC)_IDLE mode,initial access after Radio Link Failure (RLF), or handover requiringrandom access, or upon generation of UL/DL data requiring random accessin RRC_CONNECTED mode, the random access procedure is performed. Therandom access procedure is performed in a contention-based manner or anon-contention-based manner.

Referring to FIG. 8, a UE receives random access information from an eNBby system information and stores the received random access information.Subsequently, when random access is needed, the UE transmits a randomaccess preamble (message 1 or Msg1) to the eNB on a PRACH (S810). Uponreceipt of the random access preamble from the UE, the eNB transmits arandom access response message (message 2 or Msg2) to the UE (S820).Specifically, DL scheduling information for the random access responsemessage is CRC-masked by a Random Access-RNTI (RA-RNTI) and transmittedon a PDCCH. Upon receipt of the DL scheduling signal masked by theRA-RNTI, the UE may receive the random access response message on aPDSCH. Then, the UE determines whether a Random Access Response (RAR)directed to the UE is included in the random access response message.The RAR includes a Timing Advance (TA), UL resource allocationinformation (a UL grant), a temporary UE ID, etc. The UE transmits aUL-SCH message (message 3 or Msg3) to the eNB according to the UL grant(S830). After receiving the UL-SCH message, the eNB transmits acontention resolution message (message 4 or Msg4) to the UE (S840).

FIG. 9 is a conceptual diagram illustrating a CRS. Referring to FIG. 9,CRS may be transmitted through the antenna ports 0˜3. One antenna (P=0),two antennas (P=0,1), or four antennas (P=0,1,2,3) may be supportedaccording to base stations (BSs). FIG. 9 illustrates the CRS structureused when a maximum of 4 antennas is supported. In the LTE system, CRSis used not only for demodulation but also for measurement. CRS may betransmitted throughout the entire band in all DL subframes supportingPDSCH transmission, and may be transmitted through all antenna portsconfigured in the BS. In the meantime, CRS is transmitted through theentire band for each subframe, resulting in high RS overhead.

Channel Status Information Feedback

In the 3GPP LTE system, when a DL reception entity (e.g., UE) is coupledto a DL transmission entity (e.g., eNB), a Reference Signal ReceivedPower (RSRP) and a Reference Signal Received Quality (RSRQ) that aretransmitted via downlink are measured at an arbitrary time, and themeasured result may be periodically or event-triggeredly reported to theeNB.

In a cellular OFDM wireless packet communication system, each UE mayreport DL channel information based on a DL channel condition viauplink, and the eNB may determine time/frequency resources and MCS(Modulation and Coding Scheme) so as to transmit data to each UE usingDL channel information received from each UE.

In case of the legacy 3GPP LTE system (e.g., 3GPP LTE Release-8 system),such channel information may be composed of Channel Quality Indication(CQI), Precoding Matrix Indicator (PMI), and Rank Indication (RI). Allor some of CQI, PMI and RI may be transmitted according to atransmission mode of each UE. CQI may be determined by the receivedsignal quality of the UE. Generally, CQI may be determined on the basisof DL RS measurement. In this case, a CQI value actually applied to theeNB may correspond to an MCS in which the UE maintains a Block ErrorRate (BLER) of 10% or less at the measured Rx signal quality and at thesame time has a maximum throughput or performance.

In addition, such channel information reporting scheme may be dividedinto periodic reporting and aperiodic reporting upon receiving a requestfrom the eNB.

Information regarding the aperiodic reporting may be assigned to each UEby a CQI request field of 1 bit contained in uplink schedulinginformation sent from the eNB to the UE. Upon receiving the aperiodicreporting information, each UE may transmit channel informationconsidering the UE's transmission mode to the eNB over a physical uplinkshared channel (PUSCH). If necessary, RI and CQI/PMI may not betransmitted over the same PUSCH.

In case of the aperiodic reporting, a cycle in which channel informationis transmitted via an upper layer signal, an offset of the correspondingperiod, etc. may be signaled to each UE in units of a subframe, andchannel information considering a transmission (Tx) mode of each UE maybe transmitted to the eNB over a physical uplink control channel (PUCCH)at intervals of a predetermined time. In the case where UL transmissiondata is present in a subframe to which channel information istransmitted at intervals of a predetermined time, the correspondingchannel information may be transmitted together with data over not aPUCCH but a PUSCH together. In case of the periodic reporting over aPUCCH, a limited number of bits may be used as compared to PUSCH. RI andCQI/PMI may be transmitted over the same PUSCH.

If the periodic reporting collides with the aperiodic reporting, onlythe aperiodic reporting may be performed within the same subframe.

In order to calculate a WB CQI/PMI, the latest transmission RI may beused. In a PUCCH reporting mode, RI may be independent of another RI foruse in a PUSCH reporting mode. RI may be effective only at CQI/PMI foruse in the corresponding PUSCH reporting mode.

The CQI/PMI/RI feedback type for the PUCCH reporting mode may beclassified into several feedback types. Type 1 is a CQI feedback for auser-selected subband. Type 2 is a WB CQI feedback and a WB PMIfeedback. Type 3 is an RI feedback. Type 4 is a WB CQI feedback. Type 5is RI and WB PMI feedback. Type 6 is RI and PTI feedback.

Referring to Table 6, in the case of periodic reporting of channelinformation, a reporting mode is classified into four reporting modes(Modes 1-0, 1-1, 2-0 and 2-1) according to CQI and PMI feedback types.

TABLE 6 PMI Feedback Type No PMI (OL, TD, single-antenna) Single PMI(CL) CQI Wideband Mode 1-0 Mode 1-1 Feedback RI (only for Open-Loop SM)RI Type One Wideband CQI (4 bit) Wideband CQI (4 bit) when RI > 1, CQIof first codeword Wideband spatial CQI (3 bit) for RI > 1 Wideband PMI(4 bit) UE Mode 2-0 Mode 2-1 Selected RI (only for Open-Loop SM) RIWideband CQI (4 bit) Wideband CQI (4 bit) Best-1 CQI (4 bit) in each BPWideband spatial CQI (3 bit) for RI > 1 Best-1 indicator(L-bit label)Wideband PMI (4 bit) when RI > 1, CQI of first codeword Best-1 CQI (4bit) 1 in each BP Best-1 spatial CQI (3 bit) for RI > 1 Best-1 indicator(L-bit label)

The reporting mode is classified into a wideband (WB) CQI and a subband(SB) CQI according to a CQI feedback type. The reporting mode isclassified into a No-PMI and a Single PMI according to transmission ornon-transmission of PMI. As can be seen from Table 5, ‘NO PMI’ maycorrespond to an exemplary case in which an Open Loop (OL), a TransmitDiversity (TD), and a single antenna are used, and ‘Single PMI” maycorrespond to an exemplary case in which a closed loop (CL) is used.

Mode 1-0 may indicate an exemplary case in which PMI is not transmittedbut WB CQI is transmitted only. In case of Mode 1-0, RI may betransmitted only in the case of Spatial Multiplexing (SM), and one WBCQI denoted by 4 bits may be transmitted. If RI is higher than ‘1’, aCQI for a first codeword may be transmitted. In case of Mode 1-0,Feedback Type 3 and Feedback Type 4 may be multiplexed at different timepoints within the predetermined reporting period, and then transmitted.The above-mentioned Mode 1-0 transmission scheme may be referred to asTime Division Multiplexing (TDM)-based channel information transmission.

Mode 1-1 may indicate an exemplary case in which a single PMI and a WBCQI are transmitted. In this case, 4-bit WB CQI and 4-bit WB PMI may betransmitted simultaneously with RI transmission. In addition, if RI ishigher than ‘1’, 3-bit WB Spatial Differential CQI may be transmitted.In case of transmission of two codewords, the WB spatial differentialCQI may indicate a differential value between a WB CQI index forCodeword 1 and a WB CQI index for Codeword 2. These differential valuesmay be assigned to the set {−4, −3, −2, −1, 0, 1, 2, 3}, and eachdifferential value may be assigned to any one of values contained in theset and be represented by 3 bits. In case of Mode 1-1, Feedback Type 2and Feedback Type 3 may be multiplexed at different time points withinthe predetermined reporting period, and then transmitted.

Mode 2-0 may indicate that no PMI is transmitted and a CQI of aUE-selected band is transmitted. In this case, RI may be transmittedonly in case of an open loop spatial multiplexing (OL SM) only, a WB CQIdenoted by 4 bits may be transmitted. In each Bandwidth Part (BP),Best-1 CQI may be transmitted, and Best-1 CQI may be denoted by 4 bits.In addition, an indicator of L bits indicating Best-1 may be furthertransmitted. If RI is higher than ‘1’, CQI for a first codeword may betransmitted. In case of Mode 2-0, the above-mentioned feedback type 1,feedback type 3, and feedback type 4 may be multiplexed at differenttime points within a predetermined reporting period, and thentransmitted.

Mode 2-1 may indicate an exemplary case in which a single PMI and a CQIof a UE-selected band are transmitted. In this case, WB CQI of 4 bits,WB spatial differential CQI of 3 bits, and WB PMI of 4 bits aretransmitted simultaneously with RI transmission. In addition, a Best-1CQI of 4 bits and a Best-1 indicator of L bits may be simultaneouslytransmitted at each bandwidth part (BP). If RI is higher than ‘1’, aBest-1 spatial differential CQI of 3 bits may be transmitted. Duringtransmission of two codewords, a differential value between a Best-1 CQIindex of Codeword 1 and a Best-1 CQI index of Codeword 2 may beindicated. In Mode 2-1, the above-mentioned feedback type 1, feedback 2,and feedback type 3 may be multiplexed at different time points within apredetermined reporting period, and then transmitted.

In the UE selected SB CQI reporting mode, the size of BP (BandwidthPart) subband may be defined by the following table 7.

TABLE 7 System Bandwidth Subband Size k Bandwidth Parts N_(RB) ^(DL)(RBs) (J) 6-7 NA NA  8-10 4 1 11-26 4 2 27-63 6 3  64-110 8 4

Table 7 shows a bandwidth part (BP) configuration and the subband sizeof each BP according to the size of a system bandwidth. UE may select apreferred subband within each BP, and calculate a CQI for thecorresponding subband. In Table 7, if the system bandwidth is set to 6or 7, this means no application of both the subband size and the numberof bandwidth parts (BPs). That is, the system bandwidth of 6 or 7 meansapplication of only WB CQI, no subband state, and a BP of 1.

FIG. 10 shows an example of a UE selected CQI reporting mode.

N_(RB) ^(DL) is the number of RBs of the entire bandwidth. The entirebandwidth may be divided into N CQI subbands (1, 2, 3, . . . , N). OneCQI subband may include k RBs defined in Table 7. If the number of RBsof the entire bandwidth is not denoted by an integer multiple of k, thenumber of RBs contained in the last CQI subband (i.e., the N-th CQIsubband) may be determined by the following equation 1.N_(RB) ^(DL)−k·└N_(RB) ^(DL)/k┘  [Equation 1]

In Equation 1, └ ┘ represents a floor operation, and └x┘ or floor(x)represents a maximum integer not higher than ‘x’.

In addition, N_(J) CQI subbands construct one BP, and the entirebandwidth may be divided into J BPs. UE may calculate a CQI index forone preferred Best-1 CQI subband in contained in one BP, and transmitthe calculated CQI index over a PUCCH. In this case, a Best-1 indicatorindicating which a Best-1 CQI subband is selected in one BP may also betransmitted. The Best-1 indicator may be composed of L bits, and L maybe represented by the following equation 2.L=┌log₂N_(J)┐  [equation 2]

In Equation 2, ┌ ┐ may represent a ceiling operation, and ┌x┐ orceiling(x) may represent a minimum integer not higher than ‘x’.

In the above-mentioned UE selected CQI reporting mode, a frequency bandfor CQI index calculation may be determined. Hereinafter, a CQItransmission cycle will hereinafter be described in detail.

Each UE may receive information composed of a combination of atransmission cycle of channel information and an offset from an upperlayer through RRC signaling. The UE may transmit channel information toan eNB on the basis of the received channel information transmissioncycle information.

Aperiodic transmission of CQI, PMI and RI over a PUSCH will hereinafterbe described.

In case of the aperiodic reporting, RI and CQI/PMI may be transmittedover the same PUSCH. In case of the aperiodic reporting mode, RIreporting may be effective only for CQI/PMI reporting in thecorresponding aperiodic reporting mode. CQI-PMI combinations capable ofbeing supported to all the rank values are shown in the following table8.

TABLE 8 PMI Feedback Type No PMI (OL, TD, single-antenna) with PMI (CL)PUSCH CQI Wideband Mode 1-2: Multiple PMI Feedback (Wideband CQI) RIType 1^(st) Wideband CQI (4 bit) 2^(nd) Wideband CQI (4 bit) if RI > 1subband PMIs on each subband UE Selected (Subband CQI) Mode 2-0 Mode2-2: Multiple PMI RI (only for Open-Loop SM) RI Wideband CQI (4 bit) +Best-M CQI (2 bit) 1^(st) Wideband CQI (4 bit) + Best-M CQI(2 bit)Best-M index 2^(nd) Wideband CQI (4 bit) + Best-M CQI(2 bit) when RI >1, CQI of first codeword if RI > 1 Wideband PMI + Best-M PMI Best-Mindex Higher layer-configured Mode 3-0 Mode 3-1: Single PMI (subbandCQI) RI (only for Open-Loop SM) RI Wideband CQI (4 bit) + subband CQI (2bit) 1^(st) Wideband CQI (4 bit) + subband CQI when RI > 1, CQI of firstcodeword (2 bit) 2^(nd) Wideband CQI (4 bit) + subband CQI (2 bit) ifRI > 1 Wideband PMI

Mode 1-2 of Table 8 may indicate a WB feedback. In Mode 1-2, a preferredprecoding matrix for each subband may be selected from a codebook subseton the assumption of transmission only in the corresponding subband. TheUE may report one WB CQI at every codeword, and WB CQI may be calculatedon the assumption that data is transmitted on subbands of the entiresystem bandwidth (Set S) and the corresponding selected precoding matrixis used on each subband. The UE may report the selected PMI for eachsubband. In this case, the subband size may be given as shown in thefollowing table 9. In Table 9, if the system bandwidth is set to 6 or 7,this means no application of the subband size. That is, the systembandwidth of 6 or 7 means application of only WB CQI and no subbandstate.

TABLE 9 System Bandwidth Subband Size N_(RB) ^(DL) (k) 6-7 NA  8-10 411-26 4 27-63 6  64-110 8

In Table 8, Mode 3-0 and Mode 3-1 show a subband feedback configured bya higher layer (also called an upper layer).

In Mode 3-0, the UE may report a WB CQI value calculated on theassumption of data transmission on the set-S (total system bandwidth)subbands. The UE may also report one subband CQI value for each subband.The subband CQI value may be calculated on the assumption of datatransmission only at the corresponding subband. Even in the case ofRI>1, WB CQI and SB CQI may indicate a channel quality for Codeword 1.

In Mode 3-1, a single precoding matrix may be selected from a codebooksubset on the assumption of data transmission on the set-S subbands. TheUE may report one SB CQI value for each codeword on each subband. The SBCQI value may be calculated on the assumption of a single precodingmatrix used in all the subbands and data transmission on thecorresponding subband. The UE may report a WB CQI value for eachcodeword. The WB CQI value may be calculated on the assumption of asingle precoding matrix used in all the subbands and data transmissionon the set-S subbands. The UE may report one selected precoding matrixindicator. The SB CQI value for each codeword may be represented by adifferential WB CQI value using a 2-bit subband differential CQI offset.That is, the subband differential CQI offset may be defined as adifferential value between a SB CQI index and a WB CQI index. Thesubband differential CQI offset value may be assigned to any one of fourvalues {−2, 0, +1, +2}. In addition, the subband size may be given asshown in the following table 7.

In Table 8, Mode 2-0 and Mode 2-2 illustrate a UE selected subbandfeedback. Mode 2-0 and Mode 2-2 illustrate reporting of the best-Maverages.

In Mode 2-0, the UE may select the set of M preferred subbands (i.e.,best-M) from among the entire system bandwidth (set S). The size of onesubband may be given as k, and k and M values for each set-S range maybe given as shown in the following table 10. In Table 10, if the systembandwidth is set to 6 or 7, this means no application of both thesubband size and the M value. That is, the system bandwidth of 6 or 7means application of only WB CQI and no subband state.

The UE may report one CQI value reflecting data transmission only at thebest-M subbands (i.e., M selected subbands). This CQI value may indicatea CQI for Codeword 1 even in the case of RI>1. In addition, the UE mayreport a WB CQI value calculated on the assumption of data transmissionon the set-S subbands. The WB CQI value may indicate a CQI for Codeword1 even in the case of RI>1.

TABLE 10 System Bandwidth N_(RB) ^(DL) Subband Size k (RBs) M 6-7 NA NA 8-10 2 1 11-26 2 3 27-63 3 5  64-110 4 6

In Mode 2-2, the UE may select the set of M preferred subbands (i.e.,best-M) from among the set-S subbands (where the size of one subband isset to k). Simultaneously, one preferred precoding matrix may beselected from among a codebook subset to be used for data transmissionon the M selected subbands. The UE may report one CQI value for eachcodeword on the assumption that data transmission is achieved on Mselected subbands and one same selection precoding matrix is used ineach of the M subbands. The UE may report an indicator of one precodingmatrix selected for the M subbands. In addition, one precoding matrix(i.e., a precoding matrix different from the precoding matrix for theabove-mentioned M selected subbands) may be selected from among thecodebook subset on the assumption that data transmission is achieved onthe set-S subbands. The UE may report a WB CQI, that is calculated onthe assumption that data transmission is achieved on the set-S subbandsand one precoding matrix is used in all the subbands, at every codeword.The UE may report an indicator of the selected one precoding matrix inassociation with all the subbands.

CQI Definition

A CQI calculation method according to a 3GPP LTE system will bedescribed in greater detail.

In calculation of a CQI value to be reported in an uplink subframe n, aUE selects a highest CQI index from among CQI index values satisfying acondition, in which a block error rate (BLER) does not exceed 10%, ofCQI indices 1 to 15 of Table 11. For example, the UE assumes when onePDSCH TB occupying the CSI reference resource is transmitted and selectsa highest CQI index from among CQI indices 1 to 15 that disables anerror probability of the PDSCH TB to exceed 0.1. If there is no CQIindex value satisfying such a condition, the UE selects COI index 0.

TABLE 11 CQI index modulation code rate × 1024 efficiency 0 out of range1 QPSK 78 0.1523 2 QPSK 120 0.2344 3 QPSK 193 0.3770 4 QPSK 308 0.6016 5QPSK 449 0.8770 6 QPSK 602 1.1758 7 16QAM 378 1.4766 8 16QAM 490 1.91419 16QAM 616 2.4063 10 64QAM 466 2.7305 11 64QAM 567 3.3223 12 64QAM 6663.9023 13 64QAM 772 4.5234 14 64QAM 873 5.1152 15 64QAM 948 5.5547

Meanwhile, a resource used to calculate the CSI is referred to as a CSIreference resource. In the frequency domain, the CSI reference resourceis defined as a group of downlink RBs for a band in which a CQI iscalculated. When the CQI is reported in an uplink subframe n, in thetime domain, a CSI reference resource is defined as a downlink subframen-n_(CQI_ref).

In the case of periodic CSI reporting, a value n_(CQI_ref) is a smallestvalue in which a downlink subframe n-n_(CQI_ref) becomes a validdownlink subframe among 4 or more values.

In the case of aperiodic CSI reporting, a value n_(CQI_ref) is a valueenabling the CSI reference resource and a CSI request of an uplink DCIformat to be located in the same valid downlink subframe.

In the case of aperiodic CSI reporting, when a downlink subframen-n_(CQI_ref) is received after a subframe having the CSI requestincluded in the grant of a random access response and the downlinksubframe n-n_(CQI_ref) is a valid downlink subframe, n_(CQI_ref) is 4.

The subframe (i) is set as a downlink subframe in the UE, (ii) is not anMBSFN subframe except for in transmission mode 9 or 10, (iii) does notinclude DwPTS when DwPTS is equal to or less than 7680 Ts, (iv) does notbelong to the measurement gap for the UE, (v) belongs to a CSI subframeset associated with periodic CSI reporting when CSI subframe sets areconfigured in a UE in the case of periodic CSI reporting, (vi) belongsto a CSI subframe set associated with a subframe having a CSI request ofDCI when TM 10 and multiple CSI processes are configured and CSIsubframe sets for a CSI process are configured in the UE in the case ofaperiodic CSI reporting for a CSI process, in order to become a validdownlink subframe.

If there is no valid downlink subframe for the CSI reference resource,the CSI report may be omitted.

MTC (Machine Type Communication)

MTC refers to communication between machines without human intervention.MTC may diversify services and related terminals. At present, an MTCservice considered most promising is smart metering. A smart meter usedfor smart metering is at once a measuring device for measuring an amountof used electricity, water, gas, etc. and a transmission device fortransmitting various related information through a communicationnetwork. The smart meter transmits an amount of used electricity, water,gas, etc. periodically or aperiodically to a management center through acommunication network. The communication network may use a licensed bandsuch as a cellular network or an unlicensed band such as a Wi-Finetwork. For convenience, the present invention considers MTCcommunication over an LTE network.

At present, in LTE-A, various coverage enhancement (CE) schemes arebeing discussed such that an MTC UE has wide uplink/downlink coverage.For improvement of coverage of the MTC UE, repeated transmission may beused. In repeated transmission, transmission frequency may bedifferently set. That is, frequency hopping may be used to improvecoverage of the MTC UE.

Regarding an MTC service, for example, in the case of smart metering, anMTC UE should transmit data to a base station periodically. Although adata transmission period is set by a service provider, it is assumedthat the data transmission period is very long. In general, since theMTC UE mainly performs a relatively simple function, the MTC UE needs tobe economically implemented. Accordingly, bandwidth available for theMTC UE is restricted regardless of actual system bandwidth available ina network, thereby reducing buffer and decoding complexity in the MTCUE.

In other words, if the MTC UE transmits or receives a signal throughonly a part of system bandwidth of the base station, the MTC UE may beimplemented at lower cost. For example, although a system band of aspecific cell is 50 RBs, if the MTC UE transmits and receives a signalthrough a subband of 6 RBs, complexity of the MTC UE may be reduced suchthat the MTC UE may be implemented at low cost. Unlike operation systembandwidth of the cell, for example, with bandwidth reduced to 1.4 MHz,uplink/downlink operation of the MTC UE may be performed. Hereinafter, areduced band may be referred to as a narrow band or a subband.

Hereinafter, a method of performing CSI feedback when bandwidthavailable for an MTC UE is restricted will be described.

As a method of restricting bandwidth available for an MTC UE, thefollowing two methods may be considered. As a first method, a specificfrequency region in system bandwidth may be specified to be used by theMTC UE. As a second method, bandwidth which may be used by the MTC UEmay be specified through a control channel such as a PDCCH/EPDCCH and,for example, in allocation of resources, the number of allocated RBs maybe restricted.

Proposal #1

According to an embodiment, a specific frequency region in systembandwidth may be semi-statically indicated. The specific frequencyregion may be semi-statically indicated through system information suchas SIB or RRC signaling. If an application field such as smart meteringis considered, since the data size of a low-cost MTC UE is very small,the number of RBs which may be received by the MTC UE may be restricted.

Since the number of RBs which may be transmitted and received by thelow-cost MTC UE is small, upon CSI feedback, a wideband CQI/wideband PMImay be reported. For example, the MTC UE may report only the widebandCQI/wideband PMI and may not support a subband CQI/subband PMI. Forexample, in the case of periodic CSI reporting, the base station may berestricted to configure only one of Mode 1-0 or Mode 1-1 in which theMTC UE reports only the wideband CQI/wideband PMI.

Spatial multiplexing may not be supported with respect to the low-costMTC UE. A PMI reported by the MTC UE may be restricted to a PMI ofrank 1. For example, according to the LTE system, a codebook is definedper RI. In the case of a non-MTC UE, an RI is measured and a PMI isselected from a codebook corresponding to the measured RI value and isreported. However, in the case of the MTC UE, RI=1 and a PMI may beselected only from a codebook corresponding to RI=1 and may be reported.In addition, in the case of the MTC UE, if only RI=1 is available, theMTC UE may omit an RI report.

In addition, the MTC UE may assume RI=1 even when a CQI is calculated.

Meanwhile, since a PDCCH for PDSCH transmission is transmitted throughan entire system bandwidth, a wideband CQI for an entire systembandwidth may be transmitted for link adaptation of the PDCCH. This maybe implemented by aperiodic CSI feedback and periodic CSI feedback.

(1) Aperiodic CSI Feedback

At present, in the LTE standard, if system bandwidth is equal to or lessthan 7 RBs, aperiodic CSI feedback is not supported. For example, ifsystem bandwidth is equal to or less than 7 RBs, reporting of a CSIthrough a PUSCH is not supported.

In the case of the MTC UE, although the number of receivable RBs isrestricted to 7 RBs or less, aperiodic CSI feedback transmitted througha PUSCH is preferably supported, because the low-cost MTC UEperiodically transmits data and operates in an idle mode during theremaining time to minimize power consumption. Accordingly, aperiodic CSIfeedback in which the base station requests CSI feedback only ifnecessary is advantageous for minimization of power consumption of theMTC UE.

According to existing aperiodic CSI feedback, as a mode for transmittingonly a wideband CQI, there are Mode 1-0 (with no PMI), Mode 1-1 (withsingle PMI) and Mode 1-2 (with multiple PMI). In addition, Mode 2-0 fortransmitting a UE-selected subband CQI and Mode 3-0 and Mode 3-1 fortransmitting a higher layer configured subband CQI are supported.

Since all of Mode 2-0, Mode 3-0 and Mode 3-1 may support a subband CQIbut the low-cost MTC UE may not support the subband CQI, the MTC UE maytransmit a wideband CQI/wideband PMI for a specified frequency regionregardless of system bandwidth in the corresponding modes. For example,the low-cost MTC UE may transmit at least one of (i) a wideband CQI forentire system bandwidth, (ii) a wideband CQI for a restricted number ofRBs allocated to the low-cost MTC UE and (iii) a wideband PMI (ifnecessary).

In the mode for transmitting the UE-selected subband CQI, the low-costMTC UE may transmit a wideband CQI for a restricted number of RBsallocated thereto.

The wideband CQI used by the MTC UE is different from a wideband CQIused by a legacy UE (e.g., non-MTC UE). The legacy UE measures awideband CQI with respect to entire system bandwidth, but the MTC UE maymeasure a wideband CQI with respect to a restricted number of RBsallocated thereto (e.g., subbands configured for monitoring).

FIG. 11 is a diagram illustrating a wideband CQI of an MTC UE accordingto an embodiment of the present invention.

For convenience of description, assume that the entire system bandwidthincludes a total of 5 MTC subbands and MTC subbands 2 and 4 areconfigured with respect to an MTC UE. That is, the MTC UE monitors MTCsubbands 2 and 4 among a total of 5 subbands. Accordingly, the basestation transmits MTC control information or data information to the MTCUE through at least one of MTC subbands 2 and 4.

As shown in FIG. 11, when a non-MTC UE measures a wideband CQI, entiresystem bandwidth is measured. However, when the MTC UE measures awideband CQI, both of subbands 2 and 4, which are configured to bemonitored by the MTC UE, are measured.

In a mode in which a UE transmits a UE-selected subband CQI, if only awideband CQI/wideband PMI is restricted to be reported, the MTC UE doesnot need to transmit label information indicating the location of thesubband selected for CQI report and differential CQI information,thereby reducing feedback overhead.

In addition, if a wideband CQI for a restricted number of RBs is definedby a differential CQI value for entire system bandwidth, feedbackoverhead may be further reduced.

As another method, for aperiodic CSI reporting, subband CQI feedback maybe supported for the MTC UE. The subband CQI may mean that any one ofsubbands configured to be monitored by the MTC UE is measured. Forexample, in FIG. 11, when the MTC UE measures the subband CQI, a CQI forany one of subbands 2 or 4 configured to be monitored by the MTC UE maybe measured. Any one subband in which the CQI is measured may beselected by the MTC UE.

If subband CQI feedback is supported, the MTC UE may not determine asubband size based on actual system bandwidth but may determine asubband size by assuming the restricted number of RBs configured withrespect to the low-cost MTC UE as system bandwidth. For example, if theUE is configured to hop among n subbands having a size of 6 RBs and toreceive an MTC PDCCH, it may be assumed that the size of one subband inwhich the CSI will be reported is 6 RBs regardless of actual systembandwidth.

Table 12 shows a subband size which may be used by the MTC UE in higherlayer configured subband CQI feedback modes (e.g., mode 3-0, mode 3-1).

TABLE 12 Restricted number of PRBs allocated to low-cost MTC Subbandsize (number of RBs) 6-7 4  8-10 4 11-26 4 27-63 6  64-110 8

Table 13 shows the size of the subband and the number M of subbands whenthe above-described method is applied to a UE-selected subband CQIfeedback mode (e.g., mode 2-0).

TABLE 13 Restricted number of PRBs allocated Subband size (number of tolow-cost MTC RBs) M 6-7 2 1  8-10 2 1 11-26 2 3 27-63 3 5  64-110 4 8

In the above-described method, when the restricted number of RBsallocated to the MTC UE is allocated, the start points of the allocatedRB and the subband may be aligned with each other. For example, as shownin FIG. 11, when the start point of the subband always coincides withthe start point of the restricted number of RBs allocated to the MTC UE,the boundary of the subband and the boundary of the restricted number ofRBs allocated to the UE coincide with each other. In other words, theboundary of a subband (e.g., narrow band) configured such that the MTCUE transmits and receives a signal to and from the base station and theboundary of a subband configured such that the MTC UE calculates a CSImay coincide with each other.

If the start point of the allocated RB does not coincide with the startpoint of the subband, the boundary of the restricted number of RBsallocated to the MTC UE is located in the middle of the subband and thusthe MTC UE calculates or transmits a subband CQI twice before and afterthe boundary, thereby increasing the burden of the MTC UE.

(2) Periodic CSI Feedback

In periodic CSI feedback, a mode for transmitting only a wideband CQI(e.g., Mode 1-0 or Mode 1-1) may be supported. A mode (e.g., Mode 2-0 orMode 2-1) for transmitting not only a wideband CQI but also aUE-selected subband CQI may be supported for the MTC UE.

In periodic CSI feedback, the MTC UE may transmit at least one of (i) awideband CQI for entire system bandwidth, (ii) a wideband CQI for arestricted number of RBs and (iii) a wideband PMI (if necessary).

At this time, the wideband CQI for the restricted number of RBs may bedefined as a differential CQI of a wideband CQI for entire systembandwidth. In this case, feedback overhead may be reduced.

Similarly to aperiodic CSI feedback, although system bandwidth is equalto or less than 7 RBs, Mode 2-0 and Mode 2-1 may be supported for theMTC UE. In addition, a subband size and the number of bandwidth parts(BPs) may not be determined by system bandwidth but may be determinedaccording to the restricted number of RBs allocated to the low-cost MTCUE.

Table 14 shows a subband size and the number of BPs when UE-selectedsubband CQI feedback is supported for the MTC UE in periodic CSIfeedback.

TABLE 14 Restricted number of PRBs allocated Subband size to low-costMTC (number of RBs) Bandwidth part 6-7 4 1  8-10 4 1 11-26 4 2 27-63 6 3 64-110 8 4

Proposal #2

According to one embodiment of the present invention, a specificfrequency region in system bandwidth may be dynamically indicatedthrough a control channel in the MTC UE. In this case, change of anexisting CSI reporting mode may be minimized. The MTC UE may transmitonly a wideband CQI/wideband PMI (if necessary) with respect to therestricted number of RBs allocated thereto.

(1) Aperiodic CSI Feedback

In a mode (e.g., 3-0 or 3-1) for reporting a higher layer configuredsubband CQI, a subband in which a CQI will be reported may be configuredas the restricted number of RBs regardless of system bandwidth. In amode (e.g., 2-0) for reporting a UE-selected subband CQI, M=1 (i.e., onesubband) and a subband size may be configured as the restricted numberof RBs regardless of system bandwidth.

(2) Periodic CSI Feedback

In a mode (e.g., 2-0 or 2-1) for reporting a UE-selected subband CQI,the MTC UE may configure a subband size as the restricted number of RBsregardless of system bandwidth.

In addition, if a BP is configured based on a value obtained by dividingsystem bandwidth by the restricted number of RBs, a CQI value for therestricted number of RBs may be always transmitted at a reportinginstance. For example, when system bandwidth is 50 RBs and therestricted number of RBs is 6 RBs, if BP=9, a CQI value for 6 RBs may betransmitted every reporting instance.

Proposal #3

The MTC UE may use a CRS or a CSI-RS to calculate a CSI for repeatedtransmission of an MTC PDSCH. At this time, when considering that theMTC UE is located at a poor propagation environment such an interior ora basement and mobility of the MTC UE is small, channel estimationperformance may deteriorate when the MTC UE uses only a CRS or CSI-RS ofone valid subframe.

According to one embodiment of the present invention, for the MTC UE, aplurality of downlink subframes may be configured as one CSI referenceresource and thus CSI estimation performance of the MTC UE may beimproved.

In the case of periodic reporting, the MTC UE may measure a CRS or aCSI-RS transmitted in latest X1 downlink subframes (e.g., X1 validdownlink subframes) among downlink subframes located ahead by at least P(e.g., 4) subframes to perform CSI feedback. At this time, X1 may beconfigured with respect to the MTC UE through higher-layer signaling.

In the case of aperiodic reporting, the MTC UE may measure a CRS or aCSI-RS transmitted in latest X2 downlink subframes (e.g., X2 validdownlink subframes) among a plurality of downlink subframes including adownlink subframe, in which uplink grant is received, to perform CSIfeedback. At this time, X2 may be configured with respect to the MTC UEthrough higher layer signaling.

FIG. 12 is a diagram showing a set of subframes for CSI referenceresources according to an embodiment of the present invention.

The MTC UE reports a CSI in subframe # n. For convenience, assume that,among a total of k subframes from subframe # n-4 to subframe # n-k-3,three subframes # n-5, # n-6 and # n-k-3 are valid. The MTC UE mayselect a set of N subframes in order to determine a CSI referenceresource. In FIG. 12, for convenience, assume that N=2.

According to option (a), all N downlink subframes may be valid downlinksubframes. As described above, the base station may signal a higherlayer parameter for determining the number of valid subframes to beincluded in CSI reference resource to the MTC UE. According to thepresent embodiment, the higher layer parameter may be understood asindicating N.

In contrast, according to option (b), N downlink subframes may beunderstood as a time window for selecting a predetermined number ofvalid downlink subframes. For example, N downlink subframes may includeinvalid subframes. The MTC UE may select a predetermined number of validdownlink subframes from among the N downlink subframes as a CSIreference resource.

In either of option (a) or option (b), only valid subframes may beincluded in the CSI reference resource. That is, invalid subframes maynot be included in the CSI reference resource. As a result, according tooption (a), two valid downlink subframes may become the CSI referenceresource. According to option (b), one valid downlink subframe maybecome a CSI reference resource. According to option 2, N subframes maybe understood as a super set of valid downlink subframes to be selectedas a CSI reference resource.

For example, when it is assumed that the UE reports a CSI at an uplinksubframe n, the MTC UE may regard a set of a plurality of downlinksubframes (e.g., a set of valid downlink subframes) as one CSI referenceresource, thereby calculating a CSI (e.g., CQI). At this time, if anindex of a downlink located at a last position in a set of a pluralityof downlink subframes is n-nCQI_ref, nCQI_ref has a value of 4 or more.What number of downlink subframes are regarded as one CSI referenceresource may be determined based on a higher layer signaled parameter.

When the MTC UE transmits and receives a signal through only a part ofsystem bandwidth, the MTC UE may be implemented at lower cost. Forexample, although system bandwidth of a specific cell is 50 RBs, if theMTC UE transmits and receives a signal through a subband of 6 RBs,complexity of the MTU UE may be reduced and thus the MTC UE may beimplemented at low cost.

The MTC UE may be installed in a poor propagation environment (e.g., abasement, a warehouse, etc.) and generally has relatively low mobility.In order to overcome the poor propagation environment, the MTC UE mayrepeatedly transmit and receive a signal. If repeated transmission andreception of the signal is performed through only the same part ofsystem bandwidth and the frequency band is poor, performancedeterioration and battery consumption of the MTC UE may increase.Accordingly, when the frequency band in which repeated transmission isperformed is changed according to time, diversity gain can be obtainedand the number of times of repeated transmission can be reduced.Accordingly, if repeated transmission is performed with frequencyhopping, performance of the MTC UE and a battery time may increase.

When frequency hopping is configured in the MTC UE, the MTC UE mayperform CSI feedback with respect to subbands supporting frequencyhopping. For example, if system bandwidth includes subbands 1, 2 and 3and a specific signal is repeatedly transmitted and received byperforming frequency hopping with respect to subbands 1 and 2, the MTCUE may perform CSI feedback for subbands 1 and 2. Subband 3 may beexcluded from CSI feedback.

The MTC UE may consider a method of individually performing CSI feedbackwith respect to subbands for frequency hopping and a method ofperforming feedback of one CSI with respect to all subbands forfrequency hopping.

If the MTC UE individually performs CSI feedback with respect tosubbands for frequency hopping, for example, if the MTC UE calculatesand reports CSI 1 for subband 1 and CSI 2 for subband 2, the basestation may determine an entire CSI of the MTC UE with reference to theCSI transmitted per subband. The MTC UE performing CSI feedback withrespect to individual subbands may be referred to as the above-describedsubband CSI feedback.

If the MTC UE performs feedback of one CSI with respect to subbands forfrequency hopping, the MTC UE may calculate and report one CQI/PMI valuewith respect to all subbands for frequency hopping. Subbands forfrequency hopping may be regarded as subbands configured to be monitoredby the MTC UE. In addition, the MTC UE performing CSI feedback withrespect to all subbands for frequency hopping may be referred to as theabove-described wideband CSI feedback. At this time, the CSI referenceresource for measuring the CSI may be specified with respect to eachsubband. Alternatively, the MTC UE may estimate the channel of eachsubband using the CRS or CSI RS transmitted in the latest X3 subframesand generate one CQI/PMI value.

Meanwhile, as the number of subbands for frequency hopping increases,the CSI estimation performance of the MTC UE may deteriorate. Inaddition, if CSI feedback is repeatedly transmitted, CSI estimationperformance may further deteriorate.

Accordingly, a measurement report for reporting an RSRP/RSRQ rather thanaperiodic CSI feedback may be used instead of CSI feedback. To this end,the MTC UE may transmit information on a CQI/PMI in the measurementreport for reporting the RSRP/RSRQ. At this time, information on theCQI/PMI may become the MCS index of a CQI table or the PMI index of thePMI table.

Alternatively, the MTC UE may transmit information on a downlinkcoverage level (e.g., CE level)/repetition number. At this time, thebase station may determine the number of times of repeated transmission(e.g., if a coverage level is fed back) and an MCS level (e.g., ifcoverage level/repetition number is fed back) according to the coveragelevel/repetition level.

Proposal #4

As described above, for MTC CSI feedback, a plurality of subframes maybe configured as one CSI reference resource. At this time, in order forthe MTC UE to calculate a CQI, a transmission method of a PDSCHtransmitted in the plurality of subframes may be determined. If a singletransport block (TB) is transmitted through a plurality of subframes,repeated transmission may be considered from the viewpoint of codedbits. If repeated transmission of a PDSCH is assumed, the MTC UE mayassume that a redundancy version (RV) is configured in each subframe ofthe CSI reference resource as follows and calculate a CQI.

(1) Assumption 1 of RV Setting

The MTC UE may assume the same RV in the respective subframes of the CSIreference resource and calculate a CQI. This may be understood asmeaning that the MTC UE assumes that a PDSCH is repeatedly transmittedat the same coding rate. For example, the MTC UE may assume RV0 andcalculate a CQI. As RV0, that defined in TS 36.212 may be used.

(2) Assumption 2 of RV Setting

The MTC UE may assume different RVs in the respective subframes of theCSI reference resource and calculate a CQI. In this case, the CQI may becalculated on the assumption that a PDSCH assumed to be transmittedthrough a plurality of subframes of the CSI reference resource is IRcombined. Specifically, the following method (i) or (ii) may beconsidered.

(i) The MTC UE may assume that an RV (e.g., RV defined in TS 36.212) iscycled and applied to each subframe of the CSI reference resource andcalculate a CQI. For example, if four subframes are configured as theCSI reference resource, the MTC UE may assume that RV0, RV1, RV2 and RV3are applied to the respective subframes and calculate a CQI. At thistime, RVs of different orders may be configured through higherlayer/MAC/L1 signaling or may be defined in advance.

(ii) The MTC UE may assume that coded bits are continuously transmittedin the subframes corresponding to the CSI reference resource andcalculate a CQI. For example, assume that the total size of the codedbits is N, four subframes (e.g., subframes 1, 2, 3 and 4) are configuredas a CSI reference resource, and the numbers of coded bits which may betransmitted in the subframes are respectively C1, C2, C3 and C4. Thebase station may transmit coded bits corresponding to first C1 bits insubframe 1 among a total of N bits, transmit coded bits from C1+1 toC1+C2 in subframe 2, transmit coded bits from C1+C2+1 to C1+C2+C3 insubframe 3, and transmit coded bits from C1+C2+C3+1 to C1+C2+C3+C4 insubframe 4. At this time, if C1+C2 becomes greater than N, the basestation may start transmission of the coded N bits over again (e.g.,circular buffer type transmission).

(3) Assumption 3 of RV Setting

The MTC UE may assume that an RV is changed every X subframes among aplurality of subframes corresponding to a CSI reference resource andcalculate a CQI. At this time, the MTC UE assumes that the same RV ismaintained in X subframes. The RV may be changed every X subframes basedon (i) or (ii) of assumption 2 of RV setting.

Proposal #5

As described above, M (>1) subframes may be configured as a CSIreference resource. If a CQI report is performed in an uplink subframen, M subframes corresponding to the CSI reference resource forcalculating the CQI may be set as follows. The M value may be determinedbased on a higher-layer signaled parameter.

M DL subframes from a subframe n-n_(CQI ref) may be configured as a CSIreference resource. Each DL subframe of the CSI reference resource maybe a valid DL subframe.

M valid DL subframes including the subframe n-n_(CQI ref) may beconfigured as a CSI reference resource and the subframe n-n_(CQI ref)may also be a valid DL subframe, without being limited thereto. Forexample, the M DL subframes from the subframe n-n_(CQI ref) may be avalid subframe n-n_(CQI ref) and M-1 DL subframes located before thevalid DL subframe n-n_(CQI ref). In other words, the valid DL subframen-n_(CQI ref) may be a last subframe (i.e., a latest subframe) belongingto the CSI reference resource. For example, assume that M=3 and thevalid DL subframes corresponding to the CSI reference resource aresubframes n-6, n-5 and n-4. At this time, the subframe n-n_(CQI ref) maybe subframe n-4.

In contrast, the valid DL subframe n-n_(CQI ref) may be a first subframe(i.e., an oldest subframe) belonging to the CSI reference resource. Forexample, assume that M=3 and the valid DL subframes corresponding to theCSI reference resource are subframes n-6, n-5 and n-4. At this time, thesubframe n-n_(CQI ref) may be subframe n-6.

The subframe n-n_(CQI ref) may correspond to any one of the startlocation and end location of the subframes belonging to the CSIreference resource, and may be used as a reference subframe of the othersubframes belonging to the CSI reference resource. For convenience, thesubframe n-n_(CQI ref) may be referred to as a reference downlinksubframe.

FIG. 13 is a diagram illustrating a reference downlink subframeaccording to an embodiment of the present invention. Assume that theindex of the reference downlink subframe is n-n_(CQI ref) as describedabove.

According to option (1) and option (3), the reference downlink subframeis included in a set of downlink subframes for a CSI reference resource.

In contrast, according to option (2), the reference downlink subframe isexcluded from the set of downlink subframes. That is, according tooption (2), the set of downlink subframes may be located before thereference downlink subframe n-n_(CQI ref).

Specifically, according to option (1), the reference downlink subframemay be a last subframe belonging to the set of downlink subframes. Forexample, according to operation (1), the MTC UE may first determine thelocation of the reference downlink subframe n-n_(CQI ref), and select Ndownlink subframes including the reference downlink subframe backward inthe time domain.

Meanwhile, as described above, the reference downlink subframen-n_(CQI ref) be a valid downlink subframe. That is, n_(CQI ref) maymean the smallest value, in which the subframe n-n_(CQI ref) may becomea valid subframe, of four or more values. For example, in FIG. 12, thereference downlink subframe may be SF # n-5.

In addition, according to option (2), the MTC UE may first determine thelocation of the reference downlink subframe n-n_(CQI ref,) and select Ndownlink subframes located before the reference downlink subframebackward in the time domain.

In addition, according to option (3), the MTC UE may first determine thelocation of the reference downlink subframe n-n_(CQI ref,) and select Ndownlink subframes including the reference downlink subframe forward inthe time domain.

The location of the reference downlink subframe of options (1) to (3)are exemplary and the present invention is not limited thereto.

(i) In the case of periodic CSI reporting, according to option (3),n_(CQI ref) may be the smallest value of the values equal to or greaterthan M+4. That is, if the subframe n-n_(CQI ref) is a first subframeamong the subframes belonging to the CSI reference resource, n_(CQI ref)may be set to a value equal to or greater than M+4. In contrast, likeoption (1), if the subframe n-n_(CQI ref) is a last subframe of thesubframes belonging to the CSI reference resource, n_(CQI ref) may beset to a value equal to or greater than 4. Meanwhile, if the number ofvalid DL subframes is less than M, the MTC UE may drop a CSI report.

(ii) In the case of aperiodic reporting by an aperiodic CSI request of aUL DCI format, M DL subframes from a valid DL subframe in which the ULDCI format is transmitted may be configured as a CSI reference resource.At this time, if the number of valid DL subframes is less than M, theMTC UE may drop a CSI report.

(iii) If aperiodic CSI reporting is performed by an aperiodic CSIrequest included in a random access grant, according to option (3),n_(CQI ref) may be M+4. The subframe n-n_(CQI ref) may be a valid DLsubframe and may be a DL subframe after the random access grant isreceived. At this time, if the number of valid DL subframes is less thanM, the MTC UE may drop a CSI report.

As described above, M valid DL subframes from the subframe n-n_(CQI ref)may be defined as a CQI reference resource. At this time, n_(CQI ref)may be set to a value suitable for selection of M valid DL subframes.

Meanwhile, according to another embodiment of the present invention, ifthe subframe n-n_(CQI ref) is a valid DL subframe, the MTC UE may assumethat the same M DL subframes as the subframe n-n_(CQI ref) are presentand set them as a CSI reference resource. At this time, n_(CQI ref) maymean a smallest value enabling the subframe n-n_(CQI ref) to become avalid DL subframe among 4 or more values.

The above-described proposals need not to be independently implementedand may be combined as one invention.

FIG. 14 is a flowchart of a CSI reporting method according to anembodiment of the present invention. A repeated description will beomitted.

Referring to FIG. 14, the MTC UE receives a higher layer parameter froma base station (S1405). The higher layer parameter may be receivedthrough RRC signaling. The higher layer parameter may include aparameter used to determine the number of downlink subframes to beincluded in a CSI reference resource.

In addition, the MTC UE receives a CRS from the base station (S1410). Inthe subframe in which the CRS is received, an MTC PDCCH and/or an MTCPDSCH may also be received. The CRS may be received in a plurality ofsubframes. The MTC UE may perform frequency hopping with respect to aplurality of subbands. When the MTC PDCCH and/or the MTC PDSCH ismonitored or received, the MTC UE may receive the MTC PDCCH and/or theMTC PDSCH from the subbands for frequency hopping.

The MTC UE determines a CSI reference resource (S1415). For example, theMTC UE may select a set of M downlink subframes as a CSI referenceresource for the MTC UE. ‘M’ which is the number of downlink subframesto be included in the CSI reference resource may be determined based onthe higher layer parameter received from the base station.

The MTC UE measures a CSI through the CSI reference resource (S1420).CSI measurement may include a CQI (channel quality indicator). The MTCUE may measure the CQI based on a CRS (cell-specific reference signal)received through the M downlink subframes selected from the referencedownlink subframe located before the uplink subframe.

The MTC UE transmits a CSI report including the CQI to the base stationthrough an uplink subframe (S1425).

The M downlink subframes included in the CSI reference resource may bevalid downlink subframes.

The reference downlink subframe may be located before the uplinksubframe, in which the CSI report is transmitted, by at least foursubframes.

The MTC UE may be configured to repeatedly receive an MTC signal byfrequency hopping N subbands of a plurality of subbands, and the CQI maybe measured with respect to all N subbands.

The MTC UE may be configured to repeatedly receive an MTC signal byfrequency hopping N subbands of a plurality of subbands, and the CQI maybe measured with respect to any one of N subbands.

The MTC UE may assume that the same redundancy version is applied to Mdownlink subframes when one PDSCH (physical downlink shared channel)transport block is repeatedly received through M downlink subframes, andmeasure a CQI.

The MTC UE may assume that the same redundancy version is 0 and rankbetween the base station and the MTC UE is always 1, and measure a CQI.

The MTC UE may select a highest CQI index from among predetermined CQIindices in which the error probability of one PDSCH transport block doesnot exceed 0.1, when one PDSCH transport block is repeatedly receivedthrough M downlink subframes.

FIG. 15 is a diagram showing a base station and a UE applicable to anembodiment of the present invention. The base station and the UE shownin FIG. 15 may perform operation according to the above-describedembodiments.

Referring to FIG. 15, the base station 105 may include a transmission(Tx) data processor 115, a symbol modulator 120, a transmitter 125, atransmit/receive antenna 130, a processor 180, a memory 185, a receiver190, a symbol demodulator 195, and a reception (Rx) data processor 197.The UE 110 may include a Tx data processor 165, a symbol modulator 170,a transmitter 175, a transmit/receive antenna 135, a processor 155, amemory 160, a receiver 140, a symbol demodulator 155, and an Rx dataprocessor 150. Although one antenna 130 and one antenna 135 arerespectively included in the base station 105 and the UE 110, each ofthe base station 105 and the UE 110 includes a plurality of antennas.Accordingly, the base station 105 and the UE 110 according to thepresent invention support a Multiple Input Multiple Output (MIMO)system. The base station 105 and the UE 110 according to the presentinvention support both a Single User-MIMO (SU-MIMO) scheme and a MultiUser-MIMO (MU-MIMO) scheme.

In downlink, the Tx data processor 115 receives traffic data, formatsand codes the received traffic data, interleaves and modulates the codedtraffic data (or performs symbol mapping), and provides modulatedsymbols (“data symbols”). The symbol modulator 120 receives andprocesses the data symbols and pilot symbols and provides a symbolstream.

The symbol modulator 120 multiplexes data and pilot signals andtransmits the multiplexed data to the transmitter 125. At this time, thetransmitted symbols may be data symbols, pilot symbols or zero signalvalues. In each symbol period, the pilot symbols may be consecutivelytransmitted. The pilot symbols may be Frequency Division Multiplexed(FDM), Orthogonal Frequency Division Multiplexed (OFDM), Time DivisionMultiplexed (TDM) or Code Division Multiplexed (CDM) symbols.

The transmitter 125 receives and converts the symbol stream into one ormore analog signals, additionally adjusts (e.g., amplifies, filters, andfrequency-up-converts) the analog signals, and generates a downlinksignal suitable for transmission through a radio channel. Subsequently,the downlink signal is transmitted to the UE through the antenna 130.

In the UE 110, the receive antenna 135 receives the downlink signal fromthe eNB and provides the received signal to the receiver 140. Thereceiver 140 adjusts (e.g., filters, amplifies, frequency-down-converts)the received signal and digitizes the adjusted signal so as to acquiresamples. The symbol demodulator 145 demodulates the received pilotsymbols and provides the demodulated pilot symbols to the processor 155,for channel estimation.

The symbol demodulator 145 receives downlink frequency responseestimation values from the processor 155, performs data demodulationwith respect to the received data symbols, acquires data symbolestimation values (which are estimation values of the transmitted datasymbols), and provides the data symbol estimation values to the Rx dataprocessor 150. The Rx data processor 150 demodulates (that is,symbol-demaps and deinterleaves) the data symbol estimation values,decodes the demodulated values, and restores transmitted traffic data.

The processes performed by the symbol demodulator 145 and the Rx dataprocessor 150 are complementary to the processes performed by the symbolmodulator 120 and the Tx data processor 115 of the base station 105.

In the UE 110, in uplink, the Tx data processor 165 processes thetraffic data and provides data symbols. The symbol modulator 170receives the data symbols, multiplexes the data symbols, performsmodulation with respect to the symbols and provides a symbol stream tothe transmitter 175. The transmitter 175 receives and processes thesymbol stream, generates an uplink signal, and transmits the uplinksignal to the base station 105 through the transmit antenna 135.

The base station 105 receives the uplink signal from the UE 110 throughthe receive antenna 130 and the receiver 190 processes the receiveduplink signal and acquires samples. Subsequently, the symbol demodulator195 processes the samples and provides pilot symbols received in theuplink and data symbol estimation values. The Rx data processor 197processes the data symbol estimation values and restores traffic datatransmitted from the UE 110.

The respective processors 155 and 180 of the UE 110 and the base station105 instruct (e.g., control, adjust, manages, etc.) the respectiveoperations of the UE 110 and the base station 105. The processors 155and 180 may be connected to the memories 160 and 185 for storing programcodes and data. The memories 160 and 185 may be respectively connectedto the processors 155 and 180 so as to store operating systems,applications and general files.

Each of the processors 155 and 180 may also be referred to as acontroller, a microcontroller, a microprocessor, a microcomputer, etc.The processors 155 and 180 may be implemented by hardware, firmware,software, or a combination thereof. If the embodiments of the presentinvention are implemented by hardware, Application Specific IntegratedCircuits (ASICs), Digital Signal Processors (DSPs), Digital SignalProcessing Devices (DSPDs), Programmable Logic Devices (PLDs), FieldProgrammable Gate Arrays (FPGAs), etc. may be included in the processors155 and 180.

If the embodiments of the present invention are implemented by firmwareor software, the firmware or software may be configured to includemodules, procedures, functions, etc. for performing the functions oroperations of the present invention. The firmware or software configuredto perform the present invention may be included in the processors 155and 180 or may be stored in the memories 160 and 185 so as to be drivenby the processors 155 and 180.

Layers of the radio interface protocol between the UE and the eNB in thewireless communication system (network) may be classified into a firstlayer (L1), a second layer (L2) and a third layer (L3) based on thethree low-level layers of the well-known Open System Interconnection(OSI) model of a communication system. A physical layer belongs to thefirst layer and provides an information transport service through aphysical channel. A Radio Resource Control (RRC) layer belongs to thethird layer and provides control radio resources between the UE and thenetwork. The UE and the eNB exchange RRC messages with each otherthrough a wireless communication network and the RRC layer.

In the present specification, although the processor 155 of the UE andthe processor 180 of the base station perform process signals and dataexcept for a data transmission/reception function and a storage functionof the UE 110 and the base station 105, for convenience of description,the processors 155 and 180 are not specially described. Although theprocessors 155 and 180 are not specially described, the processors 155and 180 may perform a series of operations such as data processingexcept for a signal transmission/reception function and a storagefunction.

According to one embodiment of the present invention, a UE may supportMTC. A processor of the UE may select a set of M downlink subframes as aCSI reference resource for the MTC UE and measure a channel qualityindicator (CQI) through the CSI reference resource. A transmitter maytransmit a CSI report including the CQI to a base station through anuplink subframe. The number M of downlink subframes to be included inthe CSI reference resource may be determined based on a higher layerparameter received from the base station. The processor may measure theCQI based on a cell-specific reference signal (CRS) received through theM downlink subframes selected from a reference downlink subframe locatedbefore the uplink subframe.

According to one embodiment of the present invention, a base station mayreceive channel state information (CSI) reporting from a machine typecommunication (MTC) user equipment (UE). A transmitter may transmit acell-specific reference signal (CRS) through downlink subframes, undercontrol of a processor. A receiver may receive a CSI report including achannel quality indicator (CQI) measured in a CSI reference resourcefrom the MTC UE through an uplink subframe, under control of theprocessor. The CSI reference resource may be configured by M downlinksubframes among the downlink subframes in which the CRS is transmitted.The number M of downlink subframes included in the CSI referenceresource may be determined based on a higher layer parameter receivedfrom the base station. The CQI may be measured based on a cell-specificreference signal (CRS) received through the M downlink subframesselected from a reference downlink subframe located before the uplinksubframe.

The aforementioned embodiments are achieved by combination of structuralelements and features of the present invention in a predeterminedmanner. Each of the structural elements or features should be consideredselectively unless specified separately. Each of the structural elementsor features may be carried out without being combined with otherstructural elements or features. Also, some structural elements and/orfeatures may be combined with one another to constitute the embodimentsof the present invention. The order of operations described in theembodiments of the present invention may be changed. Some structuralelements or features of one embodiment may be included in anotherembodiment, or may be replaced with corresponding structural elements orfeatures of another embodiment. Moreover, it will be apparent that someclaims referring to specific claims may be combined with other claimsreferring to the other claims other than the specific claims toconstitute the embodiment or add new claims by means of amendment afterthe application is filed.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above exemplary embodiments are therefore to beconstrued in all aspects as illustrative and not restrictive. The scopeof the invention should be determined by the appended claims and theirlegal equivalents, not by the above description, and all changes comingwithin the meaning and equivalency range of the appended claims areintended to be embraced therein.

INDUSTRIAL APPLICABILITY

As described above, the embodiments of the present invention areapplicable to various wireless communication systems including a 3GPPbased wireless communication system.

The invention claimed is:
 1. A method of reporting channel stateinformation (CSI) at a machine type communication (MTC) user equipment(UE) in a wireless communication system, the method comprising:selecting a set of M downlink subframes as a CSI reference resource forthe MTC UE; selecting a subband among a set of N subbands; measuring,when frequency hopping is configured for the set of N subbands, awideband channel quality indicator (CQI) for the set of N subbands and asubband CQI for the subband through the CSI reference resource; andtransmitting the wideband CQI and the subband CQI to a base stationthrough an uplink subframe, wherein ‘M’ which is a number of thedownlink subframes to be included in the CSI reference resource isdetermined based on a higher layer parameter received from the basestation, and wherein the MTC UE measures the wideband CQI based on acell-specific reference signal (CRS) received through the M downlinksubframes which are selected from a reference downlink subframe locatedbefore the uplink subframe.
 2. The method according to claim 1, whereinthe M downlink subframes included in the CSI reference resource arevalid downlink subframes.
 3. The method according to claim 1, whereinthe reference downlink subframe is located before the uplink subframe byat least four subframes.
 4. The method according to claim 1, wherein themeasuring of the wideband CQI comprises: measuring the wideband CQI byassuming that a same redundancy version is applied to the M downlinksubframes when one physical downlink shared channel (PDSCH) transportblock is repeatedly received through the M downlink subframes.
 5. Themethod according to claim 4, wherein the measuring of the wideband CQIcomprises: measuring the wideband CQI by assuming that the sameredundancy version is 0 and rank between the base station and the MTC UEis always
 1. 6. The method according to claim 4, wherein the measuringof the wideband CQI comprises: selecting a highest CQI index value fromamong predetermined CQI indices in which an error probability of thePDSCH transport block does not exceed 0.1, when the PDSCH transportblock is repeatedly received through the M downlink subframes.
 7. Amachine type communication (MTC) user equipment (UE) for reportingchannel state information (CSI) in a wireless communication system, theMTC UE comprising: a processor configure to select a set of M downlinksubframes as a CSI reference resource for the MTC UE, select a subbandamong a set of N subbands, and measure, when frequency hopping isconfigured for the set of N subbands, a wideband channel qualityindicator (CQI) for the set of N subbands and a subband CQI for thesubband through the CSI reference resource; and a transmitter configuredto transmit the wideband CQI and the subband CQI to a base stationthrough an uplink subframe, wherein ‘M’ which is a number of thedownlink subframes to be included in the CSI reference resource isdetermined based on a higher layer parameter received from the basestation, and wherein the processor measures the wideband CQI based on acell-specific reference signal (CRS) received through the M downlinksubframes which are selected from a reference downlink subframe locatedbefore the uplink subframe.
 8. A method of receiving a channel stateinformation (CSI) report at a base station from a machine typecommunication (MTC) user equipment (UE) in a wireless communicationsystem, the method comprising: transmitting a cell-specific referencesignal (CRS) through downlink subframes; and when frequency hopping isconfigured for a set of N subbands, receiving a wideband channel qualityindicator (CQI) and a subband CQI through an uplink subframe, whereinthe subband CQI is selected among the set of N subbands by the MTC UE,wherein the wideband CQI for the set of N subbands and the subband CQIfor the subband are measured in a CSI reference resource from the MTCUE, wherein the CSI reference resource is configured as M downlinksubframes among the downlink subframes in which the CRS is transmitted,wherein ‘M’ which is a number of the downlink subframes included in theCSI reference resource is determined based on a higher layer parametertransmitted by the base station, and wherein the wideband CQI ismeasured based on a cell-specific reference signal (CRS) transmittedthrough the M downlink subframes which are selected from a referencedownlink subframe located before the uplink subframe.
 9. The methodaccording to claim 8, wherein the M downlink subframes included in theCSI reference resource are valid downlink subframes.
 10. The methodaccording to claim 8, wherein the reference downlink subframe is locatedbefore the uplink subframe by at least four subframes.
 11. The methodaccording to claim 8, wherein the wideband CQI is measured by assumingthat a same redundancy version is applied to the M downlink subframeswhen one physical downlink shared channel (PDSCH) transport block isrepeatedly transmitted through the M downlink subframes.
 12. The methodaccording to claim 11, wherein the same redundancy version is 0, and thewideband CQI is measured by assuming that rank between the base stationand the MTC UE is always 1.